1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method for producing the same. More specifically, the present invention relates to a solid electrolytic capacitor obtained by stacking valve-acting metal substrates each having a dielectric film, where a welded metal is provided in the anode part of the capacitor element. The present invention also relates to a production method therefor.
2. Description of the Related Art
With recent progress of small-size and high-frequency electronic instruments, there is a demand for a small size solid electrolytic capacitor as one of electronic parts used therefor. The response to this requirement for downsizing is generally met by a chip-form multilayer capacitor.
FIG. 1 is a perspective view showing a conventional chip-form solid electrolytic capacitor. A plurality of solid electrolytic capacitor elements 1 are disposed to lie in the same direction inside an outer jacket resin 6. The anode part 3 of the capacitor element 1 and the bottom surface of the cathode part 2 formed on the surface of the element are placed on an anode lead part 5 (as an anode lead drawing out part of a lead frame) and on a cathode lead part 4 (as a cathode lead drawing out part), respectively. Also, each is bonded to the part with an electrically conducting material such as electrically conducting adhesive. The anode lead part and the cathode lead part are paired and disposed to face each other. The thus-fabricated device is molded with a separately prepared outer jacket resin 6 such as epoxy resin.
For example, in the case where the capacitor element in a solid electrolytic capacitor has a tabular shape, a dielectric film is provided on the surface of an electrode material composed of a tabular metal having valve action, a solid electrolyte layer is provided on the dielectric film, an electrically conducting cathode layer is provided on the solid electrolyte layer to form a cathode part of the capacitor element, an anode part is integrally provided on the electrode material of the capacitor element, a resist film for masking is applied to provide a portion which becomes the anode lead part, a plurality of capacitor elements are stacked one on another such that the connection part of electrically conducting cathode layers and the connection part of anode parts come to respective corresponding positions, and the stacked body is connected to a cathode lead part and an anode lead part. By employing such a structure, the volume efficiency (capacitance value of capacitor with a fixed volume) of the capacitance of a capacitor is elevated.
In a solid electrolytic capacitor having a multilayer structure, welding which ensures stable strength is sometimes used for connecting the anode parts of a plurality of capacitor elements to the anode lead part. Known examples of the welding include resistance welding, arc welding, laser welding and ultrasonic welding.
In the case of laser welding, the anode part of the uppermost capacitor to the anode part of the lowermost capacitor element, as well as the anode lead part, must be uniformly melted. However, since the anode part (valve-acting metal) of the capacitor element usually has a melting point lower than that of the anode lead part, when a laser is irradiated to an extent sufficient to melt the anode lead part, the anode parts are melted too early. Therefore, the selection of the laser intensity and irradiation time is difficult and there is a problem that too large of a gap is produced between the anode parts or between the anode part and the anode lead part that readily causes connection failure.
Furthermore, the anode part of the capacitor element does not always show a constant laser light absorption factor. For example, in the case where the anode part is aluminum, the part irradiated with a laser hardly generates heat due to extremely low light absorption factor and despite the low melting point, the anode part is hardly melted due to high heat conductivity. Thus, the selection of laser intensity and irradiation time becomes more difficult. JP-A-8-186061 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a technique where a reflection layer having a laser reflectance of 90% or more is provided on the anode lead wire and the anode part of the capacitor element and the anode lead are welded by irradiating with a laser. However, in the case of a multilayer capacitor, anode parts of capacitor elements must be connected and a problem to be solved is present in this point.
In the case where the anode part of the capacitor element is etched, the sponge-state etched part (porous part) recovers the original density of the anode part metal when melted by a laser ray. As a result, the volume of the welding part becomes smaller than the volume before welding to disadvantageously cause welding failure.
The present inventors have made extensive studies to solve the above-described problems. As a result, the present invention provides a solid electrolytic capacitor and a production method therefor, where in using laser welding as means for connecting anode parts of capacitor elements and the anode lead part, a laser ray is irradiated after providing a weld metal on the anode part of the capacitor element, to thereby obtain a good connection between capacitor elements and between the capacitor element and the anode lead part.
More specifically, the present invention provides the following solid electrolytic capacitor and a method for producing the same:
1) a solid electrolytic capacitor comprising a molded body of a solid electrolytic capacitor element having an anode part assigned to one end part of an anode substrate composed of a valve-acting metal having on the surface thereof a dielectric film layer, and a cathode part including a solid electrolyte layer formed on the dielectric film layer in a remaining portion of the anode substrate and having an electrically conducting layer formed thereon, the anode part being connected to a lead frame via a weld metal provided on the anode part of the solid electrolytic capacitor element by irradiating the anode part with a laser ray, and said body being molded with an outer jacket resin;
2) a solid electrolytic capacitor comprising a molded body of a plurality of solid electrolytic capacitor elements each having an anode part assigned to one end part of an anode substrate composed of a valve-acting metal having on the surface thereof a dielectric film layer, and a cathode part consisting of a solid electrolyte layer formed on the dielectric film layer in the remaining portion of the anode substrate and an electrically conducting layer formed thereon, the anode parts and the cathode parts being stacked one on the other, the anode parts being connected to a lead frame via a weld metal provided on one or more of the anode part of the solid electrolytic capacitor elements by irradiating the anode parts with a laser ray, and the stacked body being molded with an outer jacket resin;
3) the solid electrolytic capacitor as described in 1 or 2 above, wherein the weld metal is interposed between the anode part of the capacitor element and the lead frame and/or between the anode parts of the solid electrolytic capacitor elements;
4) the solid electrolytic capacitor as described in any one of 1 to 3 above, wherein the weld metal is a metal capable of being melted by the laser ray;
5) the solid electrolytic capacitor as described in any one of 1 to 4 above, wherein the laser ray is a ray emitted from a YAG laser, YVO4 laser, carbon dioxide laser or Ar laser;
6) the solid electrolytic capacitor as described in any one of 1 to 5 above, wherein the weld metal is selected from the group consisting of nickel, iron, copper, aluminum, chromium, molybdenum and alloys thereof;
7) the solid electrolytic capacitor as described in any one of 1 to 6 above, wherein the valve-acting metal is selected from the group consisting of aluminum, tantalum, titanium, niobium and alloys thereof;
8) the solid electrolytic capacitor as described in any one of 1 to 6 above, wherein the valve-acting metal is an electrochemically formed aluminum foil or electrochemically formed niobium foil;
9) the solid electrolytic capacitor as described in any one of 1 to 8 above, wherein the valve-acting metal is a foil electrochemically formed at a voltage of less than 30 V;
10) the solid electrolytic capacitor as described in any one of 1 to 9 above, wherein the lead frame is a copper- or copper alloy-based material;
11) the solid electrolytic capacitor as described in any one of 1 to 10 above, wherein the solid electrolyte comprises a xcfx80-electron conjugated system polymer;
12) the solid electrolytic capacitor as described in 11 above, wherein the xcfx80-electron conjugated system polymer is a polymer obtained from a 5-membered heterocyclic compound;
13) the solid electrolytic capacitor as described in 12 above, wherein the 5-membered heterocyclic compound comprises at least one compound selected from the group consisting of pyrrole, thiophene, furan, isothianaphthene, 1,3-dihydroisothianaphthene and substitution derivatives thereof;
14) the solid electrolytic capacitor as described in 12 above, wherein the 5-membered heterocyclic compound comprises at least one compound selected from the group consisting of 3,4-ethylenedioxythiophene and 1,3-dihydroisothianaphthene;
15) a method for producing a solid electrolytic capacitor, which comprises providing an anode part at one end part of an anode substrate composed of a valve-acting metal having on the surface thereof a dielectric film layer, forming a solid electrolyte layer on the dielectric film layer in a remaining portion of the anode substrate and an electrically conducting layer thereon to provide a cathode part, thereby preparing a solid electrolytic capacitor element, providing a weld metal on the anode part, irradiating the anode part with a laser ray to connect it to a lead frame, and molding with an outer jacket resin;
16) the method for producing a solid electrolytic capacitor as described in 15 above, which comprises stacking a plurality of the solid electrolytic capacitor elements to superpose the anode parts and the cathode parts one on the other, providing a weld metal on one or more of the anode parts, irradiating the anode parts with a laser ray to connect them to a lead frame, and molding the stacked body with an outer jacket resin; and
17) the method for producing a solid electrolytic capacitor as described in 15 or 16 above, wherein the laser ray is a ray emitted from a YAG laser, YVO4 laser, carbon dioxide laser or Ar laser.